1. Field of the Invention
The present invention relates to an optical multi-axis linear displacement measurement system. More particularly, the invention is an optical multi-axis linear displacement measurement system that detects the reflected focusing light from the top surface of an object for obtaining multi-axis linear displacements of the object. The present invention also discloses an optical multi-axis linear displacement measurement method for obtaining the multi-axis linear displacements of the object.
2. Description of the Related Art
For precision positioning systems, a displacement sensor is an essential component for feedback control of the position and displacement of an object to be measured. Most conventional displacement measurement systems perform precision displacement measurement based on methods such as the optical interferometry or measurement of capacitance, magnetic flux, or tunneling current. The above-mentioned methods, however, can only be performed for measurement on single-axis linear displacement. If a user wants to perform simultaneous multi-axis displacement measurements, a plurality of displacement sensors disposed on each axis is required. Hence, the size and complexity of the mechanism and of the whole system are increased.
K. Enami et al. disclosed a system that can measure two-axis linear displacements of a metal ball, in the publication of “Nano-Probe Using Optical Sensing, by K. Enami, M. Hiraki and K. Takamasu (2000) XVI IMEKO World Congress, September 25-28, Wien, Austria.” This conventional system focused light on the center of a metal ball and the photo sensor (such as a quadrant photo diode, QPD) detected the reflected and focused light and obtained two-axis (X-Y) linear displacements of the metal ball in a plane. In addition, this conventional system should be in physical contact with the object to be measured and thus it is difficult to be used for measuring the linear displacement of a small object.
S. Usuki et al. disclosed a system that can measure three-axis linear displacements of a metal ball, in the publication of “Improving the accuracy of 3D displacement measuring using ring-shaped laser beam and high resolution CCD, by S. Usuki, K. Enami, O. Sato, S. Takahashi and K. Takamasu (2004) Proc. of 4th euspen International Conference Glasgow, Scotland (UK), May-June.” This conventional system focused light on the center of a metal ball, and the photo sensor (such as a charge-coupled device, CCD) detected the reflected and focused light and obtained a three-axis (X-Y-Z) linear displacement of the metal ball. This conventional system should also be in physical contact with the object to be measured and thus it is difficult to be used for measuring the linear displacement of a small object. In addition, it requires a complicated processing algorithm to process the data obtained with the CCD, so its response speed is very limited and cannot detect high-frequency movement of an object.
Christian Rembe et al. disclosed a system that can measure full three-dimensional displacements of MEMS component, in the publication of “Measurement System for Full Three-Dimensional Motion Characterization of MEMS, by Christian Rembe and Richard S. Muller (2002) JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 11, NO. 5, OCTOBER”. The captured interferometeric image data analyzed by digital-image processing can reconstruct the multi-axial linear changes of an object. This method requires very complicated imaging processing, and cannot be used to detect multi-axis linear displacement of the object in real time.